This invention relates to a nucleotide sequence that encodes the restriction endonuclease I-SceI. This invention also relates to vectors containing the nucleotide sequence, cells transformed with the vectors, transgenic animals based on the vectors, and cell lines derived from cells in the animals. This invention also relates to the use of I-SceI for mapping eukaryotic genomes and for in viva site directed genetic recombination.
The ability to introduce genes into the germ line of mammals is of great interest in biology. The propensity of mammalian cells to take up exogenously added DNA and to express genes included in the DNA has been known for many years. The results of gene manipulation are inherited by the offspring of these animals. All cells of these offspring inherit the introduced gene as part of their genetic make-up. Such animals are said to be transgenic.
Transgenic mammals have provided a means for studying gene regulation during embryogenesis and it differentiation, for studying the action of genes, and for studying the intricate interaction of cells in the immune system. The whole animal is the ultimate assay system for manipulated genes, which direct complex biological processes.
Transgenic animals can provide a general assay for functionally dissecting DNA sequences responsible for tissue specific or developmental regulation of a variety of genes. In addition, transgenic animals provide useful vehicles for expressing recombinant proteins and for generating precise animal models of human genetic disorders.
For a general discussion of gene cloning and expression in animals and animal cells, see Old and Primrose, xe2x80x9cPrinciples of Gene Manipulation,xe2x80x9d Blackwell Scientific Publications, London (1989), page 255 et seq.
Transgenic lines, which have a predisposition to specific diseases and genetic disorders, are of great value in the investigation of the events leading to these states. It is well known that the efficacy of treatment of a genetic disorder may be dependent on identification of the gene defect that is the primary cause of the disorder. The discovery of effective treatments can be expedited by providing an animal model that will lead to the disease or disorder, which will enable the study of the efficacy, safety, and mode of action of treatment protocols, such as genetic recombination.
One of the key issues in understanding genetic recombination is the nature of the initiation step. Studies of homologous recombination in bacteria and fungi have led to the proposal of two types of initiation mechanisms. In the first model, a single-strand nick initiates strand assimilation and branch migration (Meselson and Radding 1975). Alternatively, a double-strand break may occur, followed by a repair mechanism that uses an uncleaved homologous sequence as a template (Resnick and Martin 1976). This latter model has gained support from the fact that integrative transformation in yeast is dramatically increased when the transforming plasmid is linearized in the region of chromosomal homology (Orr-Weaver, Szostak and Rothstein 1981) and from the direct observation of a double-strand break during mating type interconversion of yeast (Strathern et al. 1982). Recently, double-strand breaks have also been characterized during normal yeast meiotic recombination (Sun et al. 1989; Alani, Padmore and Kleckner 1990).
Several double-strand endonuclease activities have been characterized in yeast: HO and intron encoded endonucleases are associated with homologous recombination functions, while others still have unknown genetic functions (Endo-SceI, Endo-SceII) (Shibata et al. 1984; Morishima et al. 1990). The HO site-specific endonuclease initiates mating-type interconversion by making a double-strand break near the YZ junction of MAT (Kostriken et al. 1983). The break is subsequently repaired using the intact HML or HMR sequences and resulting in ectopic gene conversion. The HO recognition site is a degenerate 24 bp non-symmetrical sequence (Nickoloff, Chen, and Heffron 1986; Nickoloff, Singer and Heffron 1990). This sequence has been used as a xe2x80x9crecombinatorxe2x80x9d in artificial constructs to promote intra- and intermolecular mitotic and meiotic recombination (Nickoloff, Chen and Heffron, 1986; Kolodkin, Klar and Stahl 1986; Ray et al. 1988, Rudin and Haber, 1988; Rudin, Sugarman, and Haber 1989).
The two-site specific endonucleases, I-SceI (Jacquier and Dujon 1985) and I-SceII (Delahodde et al. 1989; Wenzlau et al. 1989), that are responsible for intron mobility in mitochondria, initiate a gene conversion that resembles the HO-induced conversion (see Dujon 1989 for review). I-SceI, which is encoded by the optional intron Sc LSU.1 of the 21S rRNA gene, initiates a double-strand break at the intron insertion site (Macreadie et al. 1985; Dujon et al. 1985; (ref. 7 and ref. A4) Colleaux et al. 1986)(ref.8). The recognition site of I-SceI extends over an 18 bp non-symmetrical sequence (Colleaux et al. 1988). Although the two proteins are not obviously related by their structure (HO is 586 amino acids long while I-SceI is 235 amino acids long), they both generate 4 bp staggered cuts with 3xe2x80x2OH overhangs within their respective recognition sites. It has been found that a mitochondrial intron-encoded endonuclease, transcribed in the nucleus and translated in the cytoplasm, generates a double-strand break at a nuclear site. The repair events induced by I-Scel are identical to those initiated by HO.
In summary, there exists a need in the art for reagents and methods for providing transgenic animal models of human diseases and genetic disorders. The reagents can be based on the restriction enzyme I-SceI and the gene encoding this enzyme. In particular, there exists a need for reagents and methods for replacing a natural gene of fragment thereof, with another gene or gene fragment that is capable of alleviating the disease, or is capable, by modifying the cell or animal, to offer molecular tools to study such diseases.
Accordingly, this invention aids in fulfilling these needs in the art. Specifically, this invention relates to an isolated DNA encoding the enzyme I-SceI. The DNA has the following nucleotide sequence:
This invention also relates to a DNA sequence comprising a promoter operatively linked to the DNA sequence of the invention encoding the enzyme I-SceI.
This invention further relates to an isolated RNA complementary to the DNA sequence of the invention encoding the enzyme I-SceI and to the other DNA sequences described herein.
In another embodiment of the invention, a vector is provided. The vector comprises a plasmid, bacteriophage, or cosmid vector containing the DNA sequence of the invention encoding the enzyme I-SceI.
In addition, this invention relates to E. coli or eukaryotic cells transformed with a vector of the invention.
Also, this invention relates to transgenic animals containing the DNA sequence encoding the enzyme I-SceI and cell lines cultured from cells of the transgenic animals.
In addition, this invention relates to a transgenic organism in which at least one restriction site for the enzyme I-SceI has been inserted in a chromosome of the organism.
Further, this invention relates to a method of genetically mapping a eukaryotic genome using the enzyme I-SceI.
This invention also relates to a method for in vivo site directed recombination in an organism using the enzyme I-SceI.